Karl Fischer Moisture Content Determination

The Karl Fischer moisture determination technique is based on the fundamental reaction in which iodine is reduced by sulfur dioxide in the presence of water. This reaction gives a recognizable endpoint (color change). The three steps in this technique are: the extraction of water using a chemical solvent, anhydrous methanol, from the finely ground sample; removal of the solids through filtering; and titration of the liquid with "Fischer" reagent containing iodine, pyridine, and sulfur dioxide.

This is a popular method for moisture determination because it can be used on virtually all solid or semi-solid materials. It is often considered as the standard against which other methods are evaluated.

The reaction endpoint is determined from the color change occurring during the chemical reaction or by means of a voltametric endpoint indicator. This indicator consists of a double pin platinum electrode. An alternating current is applied across the pins and when the last traces of water have been titrated, the measured potential falls to practically zero.